Optical coherence tomography (OCT) provides real-time, objective, in-vivo, high resolution optical cross- sections of the retina and optic nerve. Recent innovations in OCT image acquisition, including the incorporation of Fourier/spectral-domain detection, have improved imaging speed, sensitivity and resolution. Still, there remain specific structures within ocular OCT images, such as retinal ganglion cells (RGCs), which are of interest to clinicians but consistently have low contrast. This makes it difficult to differentiate between surrounding layers and structures. Our goal, therefore, is to engineer molecular OCT contrast agents suitable for enhancing contrast between structures of interest in the retina in order to improve the detection and measurement of these structures that are associated with disease. We will focus on RGCs, which are lost at an accelerated rate in glaucoma. We are proposing gold nanoparticles for ophthalmic contrast agents because their design can be tailored to augment the scattering response at the same wavelengths of light used in current ophthalmic OCT imaging schemes and their surfaces can be coated with antibodies that will facilitate targeting of specific structures. Our hypotheses are that nanoparticles can be directed to retinal tissue using antibodies specific to cellular receptors and that they will improve contrast by modulating the intensity of backscattered light detected by OCT. We will initially use gold nanorods conjugated with antibodies specifically targeting the retinal ganglion cells. The optimal concentration of nanoparticles for detection by OCT will be defined by using a phantom model and the time course of circulation of particles will be determined in mice eyes. A baseline intravitreal injection of nanoparticles will be performed and a subset of mice will be evaluated at each time point (time zero, one hour, six hours, one day, three days, and one week) and fluorescence microscopy and transmission electron microscopy will be performed on excised eyes to determine the time sequence of the nanorods transportation. The biocompatibility of the nanoparticles will be evaluated by pattern electroretinogram for functional assessment, inflammatory biomarkers and histology. At each time point during this experiment, we will also evaluate the ability of our antibody-coated nanoparticles to enhance OCT signal intensity level by performing high-speed, ultrahigh resolution retinal OCT imaging on mice prior to sacrificing them for microscopic examination. We will use these OCT images to compare nanoparticle contrast enhancement over time as well as to quantify RGC thickness by image segmentation. PUBLIC HEALTH RELEVANCE: In this study we propose to design particles that will be able to attach to specific layers in the retina and through changes in optical properties enhance the appearance of the layer in optical coherence tomography. This might improve the ability to detect pathological structural changes at an early stage and might enable targeting treatment to specific retinal layers.